An information-processing system for calibrating an orientation sensor mounted on an image-pickup device calculates a relative orientation between the orientation sensor and the image-pickup device by using information about image coordinates of indices detected from a photographed image and an orientation-measurement value. At the same time, the information-processing system obtains parameters for minimizing an error between actual measured values of the image coordinates of the indices and theoretical values of the image coordinates of the indices, where the theoretical values are calculated from estimates of unknown parameters, by using a position of the image-pickup device and the relative orientation between the orientation sensor and the image-pickup device, as the unknown parameters.